Zone storage—quickly returning to a state of consistency following an unexpected event

ABSTRACT

Systems and Methods for data storage in a distributed storage network are disclosed. Unexpected errors can adversely affect consistency of both the content of a write (including the slice data), and the synchronicity between the written slices and metadata structures. To maintain consistency between these data structures, a sequencing of the order of writes and flushes to the memory devices for the different data structures may be enforced as follows: First: Slice content data is first written to the volatile memory (e.g. a cache memory) of a DS unit; Second: the Slice content data stored in volatile memory is “flushed” to a non-volatile bin (which bin is associated with a group of physical memory blocks in non-volatile memory); Third: after the flush of the slice content data to the bin (i.e. data is durable on the media device): metadata relating to the data is written.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable.

BACKGROUND OF THE INVENTION Technical Field of the Invention

This invention relates generally to computer networks, and moreparticularly to dispersed or cloud storage.

Description of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on a remote orInternet storage system. The remote or Internet storage system mayinclude a RAID (redundant array of independent disks) system and/or adispersed storage system that uses an error correction scheme to encodedata for storage.

In a RAID system, a RAID controller adds parity data to the originaldata before storing it across an array of disks. The parity data iscalculated from the original data such that the failure of a single disktypically will not result in the loss of the original data. While RAIDsystems can address certain memory device failures, these systems maysuffer from effectiveness, efficiency and security issues. For instance,as more disks are added to the array, the probability of a disk failurerises, which may increase maintenance costs. When a disk fails, forexample, it needs to be manually replaced before another disk(s) failsand the data stored in the RAID system is lost. To reduce the risk ofdata loss, data on a RAID device is often copied to one or more otherRAID devices. While this may reduce the possibility of data loss, italso raises security issues since multiple copies of data may beavailable, thereby increasing the chances of unauthorized access. Inaddition, co-location of some RAID devices may result in a risk of acomplete data loss in the event of a natural disaster, fire, powersurge/outage, etc.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) in accordance with the presentdisclosure;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present disclosure;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present disclosure;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present disclosure;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present disclosure;

FIG. 6 is a schematic block diagram of an example of slice naminginformation for an encoded data slice (EDS) in accordance with thepresent disclosure;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present disclosure;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present disclosure;

FIG. 9 is a schematic block diagram of an example of a dispersed storagenetwork in accordance with the present disclosure;

FIG. 10A is a schematic block diagram of an example of a dispersedstorage network in accordance with the present disclosure; and

FIG. 10B is a flowchart illustrating an example of a data storageprocess in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofdispersed storage (DS) computing devices or processing units 12-16, a DSmanaging unit 18, a DS integrity processing unit 20, and a DSN memory22. The components of the DSN 10 are coupled to a network 24, which mayinclude one or more wireless and/or wire lined communication systems;one or more non-public intranet systems and/or public internet systems;and/or one or more local area networks (LAN) and/or wide area networks(WAN).

The DSN memory 22 includes a plurality of dispersed storage units 36 (DSunits) that may be located at geographically different sites (e.g., onein Chicago, one in Milwaukee, etc.), at a common site, or a combinationthereof. For example, if the DSN memory 22 includes eight dispersedstorage units 36, each storage unit is located at a different site. Asanother example, if the DSN memory 22 includes eight storage units 36,all eight storage units are located at the same site. As yet anotherexample, if the DSN memory 22 includes eight storage units 36, a firstpair of storage units are at a first common site, a second pair ofstorage units are at a second common site, a third pair of storage unitsare at a third common site, and a fourth pair of storage units are at afourth common site. Note that a DSN memory 22 may include more or lessthan eight storage units 36.

DS computing devices 12-16, the managing unit 18, and the integrityprocessing unit 20 include a computing core 26, and network orcommunications interfaces 30-33 which can be part of or external tocomputing core 26. DS computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each of the managing unit 18 and the integrity processing unit20 may be separate computing devices, may be a common computing device,and/or may be integrated into one or more of the computing devices 12-16and/or into one or more of the dispersed storage units 36.

Each interface 30, 32, and 33 includes software and/or hardware tosupport one or more communication links via the network 24 indirectlyand/or directly. For example, interface 30 supports a communication link(e.g., wired, wireless, direct, via a LAN, via the network 24, etc.)between computing devices 14 and 16. As another example, interface 32supports communication links (e.g., a wired connection, a wirelessconnection, a LAN connection, and/or any other type of connectionto/from the network 24) between computing devices 12 and 16 and the DSNmemory 22. As yet another example, interface 33 supports a communicationlink for each of the managing unit 18 and the integrity processing unit20 to the network 24.

In general, and with respect to DS error encoded data storage andretrieval, the DSN 10 supports three primary operations: storagemanagement, data storage and retrieval. More specifically computingdevices 12 and 16 include a dispersed storage (DS) client module 34,which enables the computing device to dispersed storage error encode anddecode data (e.g., data object 40) as subsequently described withreference to one or more of FIGS. 3-8. In this example embodiment,computing device 16 functions as a dispersed storage processing agentfor computing device 14. In this role, computing device 16 dispersedstorage error encodes and decodes data on behalf of computing device 14.With the use of dispersed storage error encoding and decoding, the DSN10 is tolerant of a significant number of storage unit failures (thenumber of failures is based on parameters of the dispersed storage errorencoding function) without loss of data and without the need for aredundant or backup copies of the data. Further, the DSN 10 stores datafor an indefinite period of time without data loss and in a securemanner (e.g., the system is very resistant to unauthorized attempts ataccessing or hacking the data).

The second primary function (i.e., distributed data storage andretrieval) begins and ends with a DS computing devices 12-14. Forinstance, if a second type of computing device 14 has data 40 to storein the DSN memory 22, it sends the data 40 to the DS computing device 16via its interface 30. The interface 30 functions to mimic a conventionaloperating system (OS) file system interface (e.g., network file system(NFS), flash file system (FFS), disk file system (DFS), file transferprotocol (FTP), web-based distributed authoring and versioning (WebDAV),etc.) and/or a block memory interface (e.g., small computer systeminterface (SCSI), internet small computer system interface (iSCSI),etc.).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-16 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSN memory 22 fora user device, a group of devices, or for public access and establishesper vault dispersed storage (DS) error encoding parameters for a vault.The managing unit 18 facilitates storage of DS error encoding parametersfor each vault by updating registry information of the DSN 10, where theregistry information may be stored in the DSN memory 22, a computingdevice 12-16, the managing unit 18, and/or the integrity processing unit20.

The DS error encoding parameters (e.g., or dispersed storage errorcoding parameters) include data segmenting information (e.g., how manysegments data (e.g., a file, a group of files, a data block, etc.) isdivided into), segment security information (e.g., per segmentencryption, compression, integrity checksum, etc.), error codinginformation (e.g., pillar width, decode threshold, read threshold, writethreshold, etc.), slicing information (e.g., the number of encoded dataslices that will be created for each data segment); and slice securityinformation (e.g., per encoded data slice encryption, compression,integrity checksum, etc.).

The managing unit 18 creates and stores user profile information (e.g.,an access control list (ACL)) in local memory and/or within memory ofthe DSN memory 22. The user profile information includes authenticationinformation, permissions, and/or the security parameters. The securityparameters may include encryption/decryption scheme, one or moreencryption keys, key generation scheme, and/or data encoding/decodingscheme.

The managing unit 18 creates billing information for a particular user,a user group, a vault access, public vault access, etc. For instance,the managing unit 18 tracks the number of times a user accesses anon-public vault and/or public vaults, which can be used to generateper-access billing information. In another instance, the managing unit18 tracks the amount of data stored and/or retrieved by a user deviceand/or a user group, which can be used to generate per-data-amountbilling information. As will be described in more detail in conjunctionwith FIGS. 10A and 10B, usage can be determined by a managing unit 18 ona byte-hour basis.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network operations can furtherinclude monitoring read, write and/or delete communications attempts,which attempts could be in the form of requests. Network administrationincludes monitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

To support data storage integrity verification within the DSN 10, theintegrity processing unit 20 (and/or other devices in the DSN 10 such asmanaging unit 18) may assess and perform rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. Retrieved encoded slices are assessed and checked for errorsdue to data corruption, outdated versioning, etc. If a slice includes anerror, it is flagged as a ‘bad’ or ‘corrupt’ slice. Encoded data slicesthat are not received and/or not listed may be flagged as missingslices. Bad and/or missing slices may be subsequently rebuilt usingother retrieved encoded data slices that are deemed to be good slices inorder to produce rebuilt slices. A multi-stage decoding process may beemployed in certain circumstances to recover data even when the numberof valid encoded data slices of a set of encoded data slices is lessthan a relevant decode threshold number. The rebuilt slices may then bewritten to DSN memory 22. Note that the integrity processing unit 20 maybe a separate unit as shown, included in DSN memory 22, included in thecomputing device 16, managing unit 18, stored on a DS unit 36, and/ordistributed among multiple storage units 36.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the IO deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. The dispersed storage error encodingparameters include an encoding function (e.g., information dispersalalgorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment (i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R) of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides the data(e.g., a file (e.g., text, video, audio, etc.), a data object, or otherdata arrangement) into a plurality of fixed sized data segments (e.g., 1through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more).The number of data segments created is dependent of the size of the dataand the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber. In the illustrated example, the value X11=aD1+bD5+cD9,X12=aD2+bD6+cD10, . . . X53=mD3+nD7+oD11, and X54=mD4+nD8+oD12.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 80 is shown inFIG. 6. As shown, the slice name (SN) 80 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as at least part of a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

In order to recover a data segment from a decode threshold number ofencoded data slices, the computing device uses a decoding function asshown in FIG. 8. As shown, the decoding function is essentially aninverse of the encoding function of FIG. 4. The coded matrix includes adecode threshold number of rows (e.g., three in this example) and thedecoding matrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

FIG. 9 is a diagram of an example of a dispersed storage network. Thedispersed storage network includes a DS (dispersed storage) clientmodule 34 (which may be in DS computing devices 12 and/or 16 of FIG. 1),a network 24, and a plurality of DS units 36-1 . . . 36-n (which may bestorage units 36 of FIG. 1 and which form at least a portion of DSmemory 22 of FIG. 1), a DSN managing unit 18, and a DS integrityverification module (not shown). The DS client module 34 includes anoutbound DS processing section 81 and an inbound DS processing section82. Each of the DS units 36-1 . . . 36-n includes a controller 86, aprocessing module 84 (e.g. computer processor) including acommunications interface for communicating over network 24 (not shown),memory 88, a DT (distributed task) execution module 90, and a DS clientmodule 34.

In an example of operation, the DS client module 34 receives data 92.The data 92 may be of any size and of any content, where, due to thesize (e.g., greater than a few Terabytes), the content (e.g., securedata, etc.), and/or concerns over security and loss of data, distributedstorage of the data is desired. For example, the data 92 may be one ormore digital books, a copy of a company's emails, a large-scale Internetsearch, a video security file, one or more entertainment video files(e.g., television programs, movies, etc.), data files, and/or any otherlarge amount of data (e.g., greater than a few Terabytes).

Within the DS client module 34, the outbound DS processing section 81receives the data 92. The outbound DS processing section 81 processesthe data 92 to produce slice groupings 96. As an example of suchprocessing, the outbound DS processing section 81 partitions the data 92into a plurality of data partitions. For each data partition, theoutbound DS processing section 81 dispersed storage (DS) error encodesthe data partition to produce encoded data slices and groups the encodeddata slices into a slice grouping 96.

The outbound DS processing section 81 then sends, via the network 24,the slice groupings 96 to the DS units 36-1 . . . 36-n of the DSN memory22 of FIG. 1. For example, the outbound DS processing section 81 sendsslice group 1 to DS storage unit 36-1. As another example, the outboundDS processing section 81 sends slice group #n to DS unit #n.

In one example of operation, the DS client module 34 requests retrievalof stored data within the memory of the DS units 36. In this example,the task 94 is retrieve data stored in the DSN memory 22. Accordingly,and according to one embodiment, the outbound DS processing section 81converts the task 94 into a plurality of partial tasks 98 and sends thepartial tasks 98 to the respective DS storage units 36-1 . . . 36-n.

In response to the partial task 98 of retrieving stored data, a DSstorage unit 36 identifies the corresponding encoded data slices 99 andretrieves them. For example, DS unit #1 receives partial task #1 andretrieves, in response thereto, retrieved slices #1. The DS units 36send their respective retrieved slices 99 to the inbound DS processingsection 82 via the network 24.

The inbound DS processing section 82 converts the retrieved slices 99into data 92. For example, the inbound DS processing section 82de-groups the retrieved slices 99 to produce encoded slices per datapartition. The inbound DS processing section 82 then DS error decodesthe encoded slices per data partition to produce data partitions. Theinbound DS processing section 82 de-partitions the data partitions torecapture the data 92.

In one example of operation, the DSN of FIGS. 1 and 9 may be utilizedfor purposes of implementing a storage process which can facilitatequickly returning to a state of consistency following an unexpectedevent as explained below in conjunction with FIGS. 10A and 10B. Note,while these embodiments are described in the context of functionalityprovided by DS units 36, this functionality may be implemented utilizingany module and/or unit of the dispersed storage network (DSN), alone orin combination, including but not limited to DS Processing Unit 16, DSProcessing Integrity Unit 20 and/or DS Managing Unit 18. Also note,while these embodiments are described in the context of storing slicesof data, which can include dispersed storage error encoded data slices,data need not be stored in the form of slices for purposes of thestorage process described below to work.

According to one example embodiment, data slices are stored to a memorydevice (e.g. DS unit 36) by adopting a pattern of append only writes,wherein writes of data to non-volatile memory continue from a pointwhere the last write ended. One problem is Unexpected Events (UEs),which may include power off events, restarts, crashes, errors, or othersimilar unexpected events, and which can cause a disruption to one ormore of the most recent writes. This can adversely affect consistency ofboth the content of the write (including the slice data), and thesynchronicity between the written slices and related metadata structures(which can include catalogues of written slices and their size, ajournal of bin locations, and other on-memory-device data structures).To maintain consistency between these different data structures, asequencing of the order of writes and flushes to the memory devices forthe different data structures may include the following: First: Slicecontent data is first written to the volatile memory (e.g. a cachememory) of a DS unit; Second: the Slice content data stored in volatilememory is “flushed” to a non-volatile bin (which bin is associated witha group of physical memory blocks in non-volatile memory); Third: afterthe flush of the slice content data to the bin (i.e. data is durable onthe media device): metadata relating to the data is written. Metadatacan include an in-ordered log of each update operation and slice nameversion and size information. The metadata may further include pointersto the bins which may be kept in a “Journal”, and slice name and sizeinformation which may be kept in a “Catalog”, or other index informationabout the bins that are stored. Note that the writing to the differentmetadata structures (e.g. the Journal and Catalog) may be performedsequentially (and in any order), or in parallel, and at any time afterthe Slice content data is stored in the bin, even following anUnexpected event. While the specific embodiments depicted in FIGS. 10Aand 10B, and described below, involve a Journal and Catalog, these aremerely non-limiting examples, and a person of skill in the art willappreciate that metadata related to data being stored can be organizedand stored in many other ways.

If a UE occurs before the first step, no corrective action needs to takeplace because there is no slice write to be corrupted by the UE.

If the UE occurs after the first step, but before the second step, thenthere is the potential for a corrupted slice content to be written. Todetect and correct from these, an “Atomic Write Structure” is used whenthe slices are written to volatile memory in the first step. An AtomicWrite Structure is a defined structure of data written with the slicecontent data that can independently be used to recognize whether theslice content data was incompletely written, or completely written, byusing at least one verifier, which can include: “defined headers”,“length indicators”, “defined footers”, and “data checksums”. Ifverifiers are detected and verified, then the Atomic Write Structure isassumed to be valid and is accepted along with the associated slicecontent data, otherwise it is known to be invalid and is skipped. In thecase, it is skipped, there are no further recovery operations to beperformed. The area is marked as invalid and future writes continue fromthe end of where the incomplete write left off.

Otherwise, if the slice data content is validated as complete by theAtomic Write Structure, or if the UE occurred after the second step, butbefore the third step, then there is a recoverable inconsistency. Inthis case, we have a bin that contains slice data that may not bereferenced by either the catalog or the journal. In this case, theprocess determines all bin entries in bin files that are not in eitherthe journal or the catalog, and then recover both by adding theappropriate missing metadata entries based on the discovered slicecontent data. Finding these inconstancies may be optimized by looking inthe journal (i.e. performing a scan of metadata) for “safe pointmarkers”, which are references to offsets in the bins that mark the mostrecent data the journal has referenced and synchronized. The processneed only scan metadata from this offset to the write pointer—or lastappend point of the bin. Anything between the last safe point, and thewrite pointer of each bin that represents a complete write of slicecontent data is “replayed”. By replaying it brings to agreement thecontent of the bin and the journal and catalog, i.e. if the journal ismissing an item, it will be added, and if the catalog is missing anentry for that slice it will be added.

Finally, after this recovery process, the safe point can be updated (ifsafe points are used as an optimization to speed recovery).

By using this write sequence and following the above recovery procedure,there is no point in which an UE can lead to loss of slice data contentthat was successfully written to the non-volatile memory device, and nopoint in which in inconsistency between the slice content and associateddata structures cannot be corrected for slice data in either thevolatile or non-volatile memory.

An example of a dispersed storage network for storing data is shown inFIG. 10A in accordance with an embodiment. As shown therein, the networkincludes DS processing unit 16 communicably coupled via network 24 to DSunits (storage units) 36-1, 36-2, . . . 36-n, each of which unit has arespective processing module (84-1, 84-2, . . . 84-n) and a respectivememory (88-1, 88-2, . . . 88-n), which memory can be made up on one ormore physical or logical memories. As shown therein, each DS unit 36,may include a respective Bin (500-1, 500-2, . . . 500-n), a respectiveJournal (502-1, 502-2, . . . 502-n) and a respective Catalog (504-1,504-2, . . . 504-n). DS processing unit 16 sends slice content data asdata slices 508-1, 508-2, . . . 508-n to be stored in DS units 36-1,36-2, . . . 36-n respectively. As shown in more detail with respect toDS unit 36-1, memory 88-1 is made up of volatile memory (e.g., a cachememory) 88-1A and non-volatile memory 88-1B. DS units 36-2 . . . 36-ncould similarly include such volatile and non-volatile memory in theirrespective memories 88-2 . . . 88-n. An example process of storing thedata slices 508, and generating and storing metadata relating thereto,is described below in conjunction with FIG. 10B in accordance with anembodiment of the invention.

Having reference to FIG. 10B, in a step 600, data (in this specificinstance slice content data), which could be sent from DS processingunit 16 of FIG. 10A, is stored in the volatile memory of a DS unit (forexample volatile memory 88-1A of DS unit 36-1 in FIG. 10A). Next, in astep 602, the processing module 84-1 of DS unit 36-1 in FIG. 10A forexample, determines if the slice content data was completely written. Ifthe slice content data was completely written, the process continues atstep 604. Otherwise, the storing of data is incomplete and the processends. In step 604, the slice content data is “flushed” to a bin (e.g.bin 500-1 stored in non-volatile memory 84-1B of DS unit 36-1 in FIG.10A). Next, in a step 606, the processing module 84-1 of DS unit 36-1for example, determines whether metadata data has been properly written.For example, in the context of FIG. 10A, the processing module 84-1determines whether metadata relating to bin 500-1 and/or slice contentdata 508-1 is correctly written to Journal 501-1 and/or Catalog 504-1 ofDS unit 36-1. If so, the storage process is complete. Otherwise, in astep 608, if there is metadata missing, the missing metadata is stored.In the context of FIG. 10A, processing module 84-1 of DS unit 36 woulddetermine that there are bin entries in the bin files that are notproperly reflected in either the Journal 501-1 or the Catalog 504-1 ofDS. And if there are bin entries that are not in either the journal orthe catalog, the missing entries are added to the journal and/or catalogrespectively.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signalA has a greater magnitude than signal B, a favorable comparison may beachieved when the magnitude of signal A is greater than that of signal Bor when the magnitude of signal B is less than that of signal A. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from Figureto Figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information. A computer readable memory/storage medium,as used herein, is not to be construed as being transitory signals perse, such as radio waves or other freely propagating electromagneticwaves, electromagnetic waves propagating through a waveguide or othertransmission media (e.g., light pulses passing through a fiber-opticcable), or electrical signals transmitted through a wire.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method of storing data comprising: writingerror encoded slice content data to a volatile memory; flushing theerror encoded slice content data to a bin in a non-volatile memory afterdetermining the error encoded slice content data was completely writtento the volatile memory, wherein the bin is associated with a group ofphysical memory blocks in the non-volatile memory; discovering arecoverable inconsistency in the bin, where the bin contains one or moreof the encoded slice content data that is not referenced by either ametadata catalog or a metadata journal; initiating a recovery process torecover missing metadata by performing a scan of metadata for a safepoint marker, wherein the discovering a recoverable inconsistency in thebin occurs from the safe point marker to a write pointer or last appendpoint of the bin; writing a first missing metadata entry includingmissing metadata corresponding to the error encoded slice content data,after flushing the error encoded data slice content data to the bin,wherein the missing metadata is determined by recognition of bin entriesin bin files that are not in the metadata journal including pointers tothe bins or not in the metadata catalog, including an encoded slice nameand size information; and writing a second missing metadata entryincluding the missing metadata corresponding to the bin after flushingthe error encoded slice content data to the bin.
 2. The method of claim1, wherein the error encoded slice content data is flushed to the bin inthe non-volatile memory using a pattern of append only writes.
 3. Themethod of claim 1, wherein the step of writing missing metadatacorresponding to the error encoded slice content data and the step ofwriting missing metadata corresponding to the bin are performedsequentially.
 4. The method of claim 1, wherein the step of writingmissing metadata corresponding to the error encoded slice content dataand the step of writing missing metadata corresponding to the bin areperformed in parallel.
 5. The method of claim 1, wherein the errorencoded slice content data is written to the volatile memory using anatomic write structure.
 6. The method of claim 5, wherein the atomicwrite structure includes one or more of: defined headers, lengthindicators, defined footers or data checksums.
 7. The method of claim 1,further comprising the steps of: writing second error encoded slicecontent data to the volatile memory; determining that the error encodedsecond slice content data was incompletely written to the volatilememory; and marking an area of the volatile memory associated with theerror encoded second slice content data as invalid.
 8. The method ofclaim 1, further comprising updating the safe point marker after thestep of writing the missing metadata corresponding to the error encodedslice content data and the bin in the non-volatile memory after flushingthe error encoded slice content data to the bin.
 9. A dispersed storageunit for use in a dispersed storage network, the dispersed storage unitcomprising: a communications interface; a volatile memory; anon-volatile memory; and a computer processor; wherein the non-volatilememory includes instructions for causing the computer processor to:write error encoded slice content data to the volatile memory; flush theerror encoded slice content data to a bin in the non-volatile memoryafter a determination that the error encoded slice content data wascompletely written to the volatile memory, wherein the bin is associatedwith a group of physical memory blocks in the non-volatile memory;discover a recoverable inconsistency in the bin, where the bin containsone or more of the slice content data that is not referenced by either ametadata catalog or a metadata journal; initiate a recovery process torecover missing metadata by performing a scan of metadata for a safepoint marker, wherein the discover a recoverable inconsistency in thebin occurs from the safe point marker to a write pointer or last appendpoint of the bin; write a first missing metadata entry including missingmetadata corresponding to the error encoded slice content data after theerror encoded slice content data has been flushed to the bin, whereinthe missing metadata is determined by recognition of bin entries in binfiles that are not in the metadata journal including pointers to thebins or not in the metadata catalog, including an encoded slice name andsize information; and write a second missing metadata entry includingthe missing metadata corresponding to the bin after the error encodedslice content data has been flushed to the bin.
 10. The dispersedstorage unit of claim 9, wherein the non-volatile memory furthercomprises instructions for causing the computer processor to flush theerror encoded slice content data to the bin in the non-volatile memoryusing a pattern of append only writes.
 11. The dispersed storage unit ofclaim 9, wherein the non-volatile memory further comprises instructionsfor causing the computer processor to write the missing metadatacorresponding to the error encoded slice content data and instructionsfor causing the computer processor to write the missing metadatacorresponding to the bin, sequentially.
 12. The dispersed storage unitof claim 9, wherein the non-volatile memory further comprisesinstructions for causing the computer processor to write the missingmetadata corresponding to the error encoded slice content data andinstructions for causing the computer processor to write the missingmetadata corresponding to the bin, in parallel.
 13. The dispersedstorage unit of claim 9, wherein the non-volatile memory furthercomprises instructions for causing the computer processor to write theerror encoded slice content data to the volatile memory using an atomicwrite structure.
 14. The dispersed storage unit of claim 13, wherein theatomic write structure includes one or more of: defined headers, lengthindicators, defined footers or data checksums.
 15. The dispersed storageunit of claim 9, wherein the non-volatile memory further comprisesinstructions for causing the computer processor to: write second errorencoded slice content data to the volatile memory; determine that thesecond error encoded second slice content data was incompletely writtento the volatile memory; and mark an area of the volatile memoryassociated with the second error encoded slice content data as invalid.16. A dispersed storage network comprising: a plurality of dispersedstorage units; a dispersed storage processing unit wherein a firstdispersed storage unit of the plurality of dispersed storage unitsincludes: a volatile memory; a non-volatile memory; and a computerprocessor; wherein the non-volatile memory includes instructions forcausing the computer processor to: write error encoded slice contentdata to the volatile memory; flush the error encoded slice content datato a bin in the non-volatile memory after a determination that the errorencoded slice content data was completely written to the volatilememory, wherein the bin is associated with a group of physical memoryblocks in the non-volatile memory; discover a recoverable inconsistencyin the bin, where the bin contains one or more of the slice content datathat is not referenced by either a metadata catalog or a metadatajournal; initiate a recovery process to recover missing metadata byperforming a scan of metadata for a safe point marker, wherein thediscover a recoverable inconsistency in the bin occurs from the safepoint marker to a write pointer or last append point of the bin; write afirst missing metadata entry including missing metadata corresponding tothe error encoded slice content data after the error encoded slicecontent data has been flushed to the bin, wherein the missing metadatais determined by recognition of bin entries in bin files that are not inthe metadata journal including pointers to the bins or not in themetadata catalog, including an encoded slice name and size information;and write a second missing metadata entry including missing metadatacorresponding to the bin after the error encoded slice content data hasbeen flushed to the bin.
 17. The dispersed storage network of claim 16,wherein the non-volatile memory further comprises instructions forcausing the computer processor to flush the error encoded slice contentdata to the bin in the non-volatile memory using a pattern of appendonly writes.